1. Technical Field of the Invention
The present invention pertains in general to the planning and deployment of cells in a cellular telephone network, and more particularly, to restricting the operation of cellular telephones to well delineated geographical areas.
2. Description of Related Art
In the planning and deployment of a cellular telephone network, the geographical service area to be covered by the cellular telephone network is partitioned into a plurality of cells in order to facilitate frequency re-use. While in operation, a cellular telephone continually compares received signal strengths from base stations in cells adjacent to the cellular telephone. Typically, the cellular telephone establishes communication with the base station having the strongest signal. As the cellular telephone moves about the service area. Signal strengths from the base stations vary and eventually the cellular telephone reselects a new base station or, if on call, is handed-off from the current base station servicing the cellular telephone to a base station now having a stronger signal. The exact geographical location where the reselection or hand-off occurs varies with the prevailing conditions in the physical environment with respect to the propagation of radio waves. This inexact demarcation between cells creates what may be called soft-edge cells. Furthermore, since the distance from which a cellular telephone can communicate with a base station varies, the service area of a cellular telephone network cannot have an exact geographical demarcation.
In certain locations it is desirable to prohibit the operation of cellular telephones. For example, the use of cellular telephones is currently prohibited in an airplane while the airplane is preparing for take-off since transmissions from the cellular telephone can interfere with the operation of the airplane. Although cellular telephone network providers can attempt to locate cell sites away from prohibited locations such as airport runways, it is unlikely that cellular telephone service can be excluded from the geographical location of the airport runway while at the same time providing service to geographical areas adjacent to the runway due the nature of soft-edge cells. It would be advantageous therefore, to develop a method and apparatus to create hard-edge cells where the ability to operate a cellular telephone is based on the geographical coordinates where the cellular telephone is located and not on the transmission distance of radio waves.